How is everyone using this setting? Do you set it unique for each site or for all sites have GroupA and GroupB to allow ABAB reuse?
We are using a FQDN type approach. Example: 1234-twr-1, 1234-wtr-2. Whereas 1234 is site name, twr is tower and wtr is water tower, numerals 1 and 2 are frequency reuse group ID. You may have group 1 on north and south facing APs and 2 on East, West and on a neighboring site flip that grouping to fit.
Reading this it appears to be that you should try to have as few unique IDs as possible.
We just use A B C D E F and any radios that are using the same frequencies have the same reuse ID. When this feature is fully implemented I believe it should exclude the same reuse ID from interference calculations.